Variable temperature curable composition

ABSTRACT

Curable composition comprising at least one polyaromatic having reactive end groups, at least one thermoset resin, and a reactive catalyst, wherein the reactive end groups are adapted to react with the catalyst, characterized in that the catalyst comprises a Lewis acid having amine functionality, suitably the catalyst is of the formula: LXn.R where LXn is a Lewis acid and R is a amine; process for the preparation thereof; method for curing thereof; cured products and prepreg; and method for cure cycle design.

The present invention relates to a variable temperature curablecomposition, the process for the preparation thereof, method for curingthereof, a cured neat resin, pre-preg, composite and shaped article, anda method for selecting a temperature time profile for curing a variabletemperature curable composition. More particularly the present inventionrelates to a low temperature or rapid cure variable temperature curableresin composition comprising a reactive thermoplast resin and a reactivecatalyst, the cured resin, pre-preg, composite, shaped product, and aprocess for the preparation, precuring and post curing thereof and amethod for selecting a temperature time profile for curing a variabletemperature curable composition.

For the production of engineering grade materials such as compoites andadhesives characterised by advanced mechanical properties, curable resincompositions comprising in combination a thermoplast and thermosetcomponent are typically cured in an autoclave at elevated temperatureand pressure for a sufficient period to allow reaction leading to anincrease in molecular weight and glass transition temperature (Tg). Thecuring must be carried out for a sufficient period to allow these andother mechanical properties to develop.

There are two main opportunities in adopting low temperature curing(LTC) firstly the use of cheaper tooling materials which are lightweight i.e. replacing steel with aluminium. This is possible because theLTC means that thermal expansion coefficient differences between thecomposite and aluminium are not as critical as at high temperature.

Secondly, closer dimensional tolerances are achievable which is veryimportant in constructing high quality multicomponent structures andmatching component parts together avoiding strains but providing a goodfit.

Low temperature curing however requires extended periods for curing. Incases in which curing is conducted in an autoclave, or in production ofcured parts at high turnover rate, the extended periods required forcuring may be unacceptable. In such case it may be simply a matter ofincreasing the cure temperature, but this is not possible in all casesor is not effective with some catalysts.

There remains a need for a thermoplast resin-containing compositionwhich can be cured at low temperatures. A number of low temperaturecuring catalysts are useful in other systems, such as imidazole and ureabased low temperature cure catalysts. However on testing these in thepresent composition, these were found to give inferior properties anddid not sufficiently develop the glass transition temperature, even onextended post curing. There is also a need for a catalyst which iseffective for rapid curing.

We have now surprisingly found that a thermoplast thermoset resincontaining composition may be provided which is curable at variabletemperatures and for variable cure periods and provides cured productshaving acceptable properties. The composition of the invention iscurable for example at low temperature at which it has moreoversurprisingly been found that the cured product displays comparable orsuperior properties in comparison with conventional cured compositions.It has moreover been found that the use of the low temperature cure in anovel process comprising a pre-cure and a post cure leads to furtheradvantages in terms of processing and properties. We have moreover foundthat the use of a high temperature cure in a single stage leads todesired rapid cure and turnover.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 is graph showing the consumption of epoxy for X99 cured atdifferent temperatures as a function of time.

FIG. 2 is graph showing the development of ether linkages for X99curedat different temperatures as a function of time.

FIG. 3 a is graph showing the exothermal sweep of X99 at differenttemperatures as a function of time.

FIG. 3 b is graph showing the gel time for X99 cured at differenttemperatures as a function of time.

FIG. 4 is graph showing Dichloromethane solvent uptake forX99+0.6BF3(mea) at 25° C. as a function of time.

FIG. 5 is graph showing water solvent uptake for X99+0.6BF3(mea) at 25°C. as a function of time.

FIG. 6 is graph showing Methyl Ethyl Ketone solvent uptake forX99+0.6BF3(mea) at 25° C. as a function of time.

FIG. 7 is graph showing the pre-cured Tg's of the Boron Triflouridecatalysts used to cure X99 as a function of pre-cure time in hours.

FIG. 8 is graph showing the post-cure Tg's of the materials shown inFIG. 7.

FIG. 9 is graph showing the level of consumption of epoxide generatedfrom the data in Table XI as a function of time at 85° C.

FIG. 10 is graph showing the level of ether generated from the data inTable XII as a function of time at 85° C.

FIG. 11 is graph showing the results for pre-cured Tg's as a function oftime at 85° C.

FIG. 12 is graph showing the results for post-cured Tg's of thepre-cured materials shown in FIG. 11 as a function of time at 85° C.

In its broadest aspect there is provided according to the presentinvention a curable composition comprising a polyaromatic havingreactive end groups, a thermoset resin, and a reactive catalyst, whereinthe reactive end groups are adapted to react with the catalyst.

The catalyst comprises a Lewis acid having amine functionality.Preferably the catalyst is of the formula:LXn—RWhere LXn is a Lewis acid and R is an amine. Preferably L is selectedfrom Groups IIb, IIIb, VIII of the Periodic Table of the Elements and Xis halo.

Preferred catalysts include BF₃, AlF₃, FeF₃, ZnF₂ as Lewis acidcomponent and primary or secondary aliphatic or aromatic amine such asmonoethyl amine (mea), dimethylamine (dma), benzylamine (bea) orpiperidine. It is thought that the Lewis acid catalyst is present as acomplex or equivalent form which is capable of co-ordinating thereactive end groups of the thermoplast resin with a thermoset resin. Theparticular Lewis acid complexes of the invention are found to have botha reactive and moderating function whereby the pre-cure reaction has therequired selectivity. Without being limited to this theory it is thoughtthat two possible reactions can occur in the curable composition, thereaction between reactive groups of the respective thermoplast andthermoset resin components and the reaction between respective groups ofonly one of these, for example the reaction between amine group and anepoxy group, or the reaction between an epoxy and a hydroxyl groupderived from the ring opening reaction of another epoxy group. Thereaction between thermoplast and thermoset resin would be termed chaingrowth, whereas the self reaction for example of the thermoset would besimply a monophase reaction, in this case of etherification.

It is believed that chain growth dominates the catalytic reactions inthe composition of the present invention and helps to promote the chainextension reaction between low molecular weight fractions of thethermoplast polymer. The result would be a controlled build up in theoverall molecular weight distribution of the polymer which would lead tophase separation.

The composition may comprise additional components which areconventional in the art. Preferably the composition comprises one ormore additional catalyst or curing agents.

The additional curing agent is suitably selected from any known curingagents, for example as disclosed in EP-A-0 311 349, EPA 91310167.1,EP-A-0 365 168 or in PCT/GB95/01303, which are incorporated herein byreference, such as an amino compound having a molecular weight up to 500per amino group, for example an aromatic amine or a guanidinederivative. Particular examples are 3,3′- and4-,4′-diaminodiphenylsulphone, (available as “DDS” from commercialsources), methylenedianiline,bis(4-amino-3,5-dimethylphenyl)-1,4diisopropylbenzene (available as EPON 1062 from Shell Chemical Co);bis(4-aminophenyl)-1,4-diisopropylbenzene (available as EPON 1061 fromShell Chemical Co); 4-chlorophenyl-N,N-dimethyl-urea, eg Monuron;3,4-dichlorophenyl-N,N-dimethyl-urea, eg Diuron and dicyanodiamide(available as “Amicure CG 1200 from Pacific Anchor Chemical). Otherstandard epoxy curing agents such as aliphatic diamines, amides,carboxylic acid anhydrides, carboxylic acids and phenols can be used ifdesired. If a novolak phenolic resin is used as the main thermosetcomponent a formaldehyde generator such as hexamethylenetetraamine (HMT)is typically used as a curing agent.

It is stated in PCT/GB99/00540 for example, and as described in EP-A-0311 349 or in PCT/GB95/01303, a catalyst for the epoxy resincomponent/curing agent reaction may also be used, typically a Lewis acidor a base. The present invention differs both in the selection of Lewisacid, having moderating complex function as described above, and in thechoice of reactive polyaromatic component.

Preferably the at least one polyaromatic comprises repeating units ofthe formula.

wherein each A independently is selected from a direct link, SO₂,oxygen, sulphur, —CO— or a divalent hydrocarbon radical;

R is any one or more substituents of the aromatic rings, eachindependently selected from hydrogen, C₁₋₈ branched or straight chainaliphatic saturated or unsaturated aliphatic groups or moietiesoptionally comprising one or more heteroatoms selected from O, S, N, orhalo for example Cl or F; and groups providing active hydrogenespecially OH, NH₂, NHR— or —SH, where R— is a hydrocarbon groupcontaining up to eight carbon atoms, or providing other cross-linkingactivity especially epoxy, (meth) acrylate, cyanate, isocyanate,acetylene or ethylene, as in vinyl, allyl or maleimide, anhydride,oxazoline and monomers containing saturation; and wherein said at leastone polyaromatic comprises reactive pendant and/or end groups.

More preferably the at least one polyaromatic comprises at least onepolyaryl sulphone comprising ether-linked repeating units, optionallyadditionally comprising thioether-linked repeating units, the unitsbeing selected from the group consisting of—(PhSO₂Ph )_(n)—and optionally additionally—(Ph)_(a)—wherein Ph is phenylene, n=1 to 2, a=1 to 3 and can be fractional andwhen a exceeds 1, said phenylenes are linked linearly through a singlechemical bond or a divalent group other than —SO₂— or are fusedtogether, provided that the repeating unit—(PhSO₂Ph)_(n)— is alwayspresent in said at least one polyarylsulphone in such a proportion thaton average at least two of said units —(PhSO₂Ph)_(n)— are in sequence ineach polymer chain present, said at least one polyarylsulphone havingreactive pendant and/or end groups.

Preferably the polyaromatic comprises polyether sulphone, morepreferably a combination of polyether sulphone and of polyether ethersulphone linked repeating units, in which the phenylene group is meta-or para- and is preferably para and wherein the phenylenes are linkedlinearly through a single chemical bond or a divalent group other thansulphone, or are fused together. By “fractional” reference is made tothe average value for a given polymer chain containing units havingvarious values of n or a.

Additionally, as also discussed, in said at least one polyarylsulphone,the relative proportions of the said repeating units is such that onaverage at least two units (PhSO₂Ph)_(n) are in immediate mutualsuccession in each polymer chain present and is preferably in the range1:99 to 99:1, especially 10:90 to 90:10, respectively. Typically theratio is in the range 25-50 (Ph)_(a), balance (PhSO₂Ph)_(n). Inpreferred polyarylsulphones the units are:1 XPhSO₂PhXPhSO₂Ph (“PES”)and11 X(Ph)_(a)XPhSO₂Ph (“PES”)where X is O or S and may differ from unit to unit; the ratio is 1 to 11(respectively) preferably between 10:90 and 80:20 especially between10:90 and 55:45.

The preferred relative proportions of the repeating units of thepolyarylsulphone may be expressed in terms of the weight percent SO₂content, defined as 100 times (weight of SO₂)/(weight of average repeatunit). The preferred SO₂ content is at least 22, preferably 23 to 25%.When a=1 this corresponds to PES/PEES ratio of at least 20:80,preferably in the range 35:65 to 65:35.

The above proportions refer only to the units mentioned. In addition tosuch units the polyarylsulphone may contain up to 50 especially up to25% molar of other repeating units: the preferred SO₂ content ranges (ifused) then apply to the whole polymer. Such units may be for example ofthe formulaR—Ph—A—Ph—Ras hereinbefore defined, in which A is a direct link, oxygen, sulphur,—CO— or a divalent hydrocarbon radical. When the polyarylsulphone is theproduct of nucleophilic synthesis, its units may have been derived forexample from one or more bisphenols and/or corresponding bisthiols orphenol-thiols selected from hydroquinone, 4,4′-dihydroxybiphenyl,resorcinol, dihydroxynaphthalene (2,6 and other isomers),4,4′-dihydroxybenzophenone, 2,2′-di(4-hydroxyphenyl)propane and-methane.

If a bis-thiol is used, it may be formed in situ, that is, a dihalide asdescribed for example below may be reacted with an alkali sulphide orpolysulphide or thiosulphate.

Other examples of such additional units are of the formula—Ph—Q (Ar—Q′)_(n)—Ph—in which Q and Q′, which may be the same or different, are CO or SO2; Aris a divalent aromatic radical; and n is 0, 1, 2, or 3, provided that nis not zero where Q is SO2. Ar is preferably at least one divalentaromatic radical selected from phenylene, biphenylene or terphenylene.Particular units have the formula—Ph—Q—{—(—Ph—)_(m)—Q′—}_(n)—Ph—where m is 1, 2 or 3. When the polymer is the product of nucleophilicsynthesis, such units may have been derived from one or more dihalides,for example selected from 4,4′-dihalobenzophenone,4,4′bis(4-chlorophenylsulphonyl)biphenyl, 1,4,bis(4-halobenzoyl)benzeneand 4,4′-bis(4-halobenzoyl)biphenyl.

They may of course have been derived partly from the correspondingbisphenols.

The polyaromatic may be the product of nucleophilic synthesis fromhalophenols and/or halothiophenols. In any nucleophilic synthesis thehalogen if chlorine or bromine may be activated by the presence of acopper catalyst.

Such activation is often unnecessary if the halogen is activated by anelectron withdrawing group. In any event fluoride is usually more activethan chloride. Any nucleophilic synthesis of the polyaromatic is carriedout preferably in the presence of one or more alkali metal salts, suchas KOH, NaOH or K₂CO₃ in up to 10% molar excess over the stoichiometric.

As previously mentioned, said at least one polyaromatic containsreactive end groups and/or pendant groups. End groups may be obtained bya reaction of monomers or by subsequent conversion of product polymersprior to or subsequently to isolation. Preferably groups are of formula—A′—Y where A′ is a divalent hydrocarbon group, preferably aromatic, andY is a group reactive with epoxide groups or with curing agent or withlike groups on other polymer molecules. Examples of Y are groupsproviding active hydrogen especially OH, NH₂, NHR′ or —SH, where R′ is ahydrocarbon group containing up to 8 carbon atoms, or providing othercross-linking reactivity especially epoxy, (meth)acrylate, cyanate,isocyanate, acetylene or ethylene, as in vinyl, allyl or maleimide,anhydride, oxazaline and monomers containing saturation. Preferred endgroups include amine and hydroxyl.

The number average molecular weight of the polyaromatic is suitably inthe range 2000 to 60000. A useful sub-range is over 9000 especially over10000 for example 11000 to 25000, or is under 9000, especially in therange of 3000 to 11000, for example 3000 to 9000, and structurally aswell as by chemical interaction increases toughness by comparison withthat of the thermoset resin alone by providing zones of the toughthermoplast between cross-linked thermset zones.

Thermoset polymers may be selected from the group consisting of an epoxyresin, an addition-polymerisation resin, especially a bis-maleimideresin, a formaldehyde condensate resin, especially a formaldehyde-phenolresin, a cyanate resin, an isocyanate resin, a phenolic resin andmixtures of two or more thereof, and is preferably an epoxy resinderived from the mono or poly-glycidyl derivative of one or more of thegroup of compounds consisting of aromatic diamines, aromatic monoprimaryamines, aminophenols, polyhydric phenols, polyhydric alcohols,polycarboxylic acids and the like, or a mixture thereof, a cyanate esterresin or a phenolic resin. Examples of addition-polymerisation resinsare acrylics, vinyls, bis-maleimides, and unsaturated polyesters.Examples of formaldehyde condensate resins are urea, melamine andphenols.

Preferably the thermoset polymer comprises at least one epoxy, cyanateester or phenolic resin precursor, which is liquid at ambienttemperature for example as disclosed in EP-A-0 311 349, EP-A-0 365 168,EPA 91310167.1 or in PCT/GB95/01303. Preferably the thermoset is anepoxy resin.

An epoxy resin may be selected from N,N,N′N′-tetraglycidyl diaminodiphenylmethane (eg “MY 9663”, “MY 720” or “MY 721” sold by Ciba-Geigy)viscosity 10-20 Pa s at 50° C.; (MY 721 is a lower viscosity version ofMY720 and is designed for higher use temperatures);N,N,N′,N′-tetraglycidyl-bis(4-aminophenyl)-1,4-diiso-propylbenzene (egEpon 1071 sold by Shell Chemical Co) viscosity 18-22 Poise at 110° C.;N,N,N′,N′-tetraglycidyl-bis(4-amino-3,5-dimethylphenyl)-1,4-diisopropylbenzene,(eg Epon 1072 sold by Shell Chemical Co) viscosity 30-40 Poise at 110°C.; triglycidyl ethers of p-aminophenol (eg “MY 0510” sold byCiba-Geigy), viscosity 0.55-0.85 Pa s at 25° C.; preferably of viscosity8-20 Pa at 25° C.; preferably this constitutes at least 25% of the epoxycomponents used; diglycidyl ethers of bisphenol A based materials suchas 2,2-bis(4,4′-dihydroxy phenyl) propane (eg “DE R 661” sold by Dow; or“Epikote 828” sold by Shell), and Novolak resins preferably of viscosity8-20 Pa s at 25° C.; glycidyl ethers of phenol Novolak resins (eg “DEN431” or “DEN 438” sold by Dow), varieties in the low viscosity class ofwhich are preferred in making compositions according to the invention;digylcidyl 1,2-phthalate, eg GLY CEL A-100; diglycidyl derivative ofdihydroxy diphenyl methane (Bisphenol F) (eg “PY 306” sold by CibaGeigy) which is in the low viscosity class. Other epoxy resin precursorsinclude cycloaliphatics such as 3′,4′-epoxycyclohexyl-3,-4-epoxycyclohexane carboxylate (eg “CY 179” soldby Ciba Geigy) and those in the “Bakelite” range of Union CarbideCorporation.

A cyanate ester resin may be selected from one or more compounds of thegeneral formula NCOAr(Y_(x)Ar_(m))_(q)OCN and oligomers and/orpolycyanate esters and combinations thereof wherein Ar is a single orfused aromatic or substituted aromatics and combinations thereof andtherebetween nucleus linked in the ortho, meta and/or para position andx=0 up to 2 and m and q=0 to 5 independently. The Y is a linking unitselected from the group consisting of oxygen, carbonyl, sulphur, sulphuroxides, chemical bond, aromatic linked in ortho, meta and/or parapositions and/or CR₁R₂ wherein R₁ and R₂ are hydrogen, halogenatedalkanes, such as the fluorinated alkanes and/or substituted aromaticsand/or hydrocarbon units wherein said hydrocarbon units are singularlyor multiply linked and consist of up to 20 carbon atoms for each R₁and/or R₂ and P(R₃R₄R′₄R₅) wherein R₃ is alkyl, aryl, alkoxy or hydroxy,R′₄ may be equal to R₄ and a singly linked oxygen or chemical bond andR₅ is doubly linked oxygen or chemical bond or Si(R₃R₄R′₄R₆) wherein R₃and R₄, R′₄ are defined as in P(R₃R₄R′₄R₅) above and R₅ is definedsimilar to R₃ above. Optionally, the thermoset can consist essentiallyof cyanate esters of phenol/formaldehyde derived Novolaks ordicyclopentadiene derivatives thereof, an example of which is XU71787sold by the Dow Chemical Company.

A phenolic resin may be selected from any aldehyde condensate resinsderived from aldehydes such as methanal, ethanal, benzaldehyde orfurfuraldehyde and phenols such as phenol, cresols, dihydric phenols,chlorphenols and C₁₋₉ alkyl phenols, such as phenol, 3- and 4-cresol(1-methyl, 3- and 4-hydroxy benzene), catechol (2-hydroxy phenol),resorcinol (1,3-dihydroxy benzene) and quinol (1,4-dihydroxy benzene).Preferably phenolic resins comprise cresol and novolak phenols.

The thermoset polymer is suitably the product of at least partly curinga resin precursor using a curing agent and optionally a catalyst.

The weight proportion of thermoplast component in the composition istypically in the range 5 to 100%, preferably 5 to 90%, especially 5 to50, for example 5 to 40%. In a particular advantage of the invention theweight proportion of thermoplast component may be selected in the range10 to 30% for desired level of tack in the final composition.

The respective components may be present in any amounts which aresuitable for the reaction thereof. Preferably the thermoset andthermoplast resin components are present in amounts respectively of15-75 parts by weight and in appropriate stoichiometry.

Preferably the thermoplast resin or the thermoplast resin and additionreactive amine containing component (DDS) are present in an amount of35-55, more preferably 40-50 parts by weight and the epoxy component ispresent in an amount of 45-75, preferably 50-60 parts by weight.

The Lewis acid catalyst is present in catalytic effective amount in therange of 0.1-5.0 parts by weight, depending on the catalyst of choice.More preferably the catalyst is present in an amount of 0.2.-3.0 partsby weight.

A resin composition is particularly suitable for fabrication ofstructures, including load-bearing or impact resisting structures. Forthis purpose it may contain a reinforcing agent such as fibres. Fibrescan be added short or chopped typically of mean fibre length not morethan 2 cm, for example about 6 mm. Alternatively, and preferably, thefibres are continuous and may, for example, be unidirectionally-disposedfibres or a woven fabric, ie the composite material comprises a prepreg.Combinations of both short and/or chopped fibres and continuous fibresmay be utilised. The fibres may be sized or unsized. Fibres can be addedtypically at a concentration of 5 to 35, preferably at least 20%, byweight. For structural applications, it is preferred to use continuousfibre for example glass or carbon, especially at 30 to 70, moreespecially 50 to 70% by volume.

The fibre can be organic, especially of stiff polymers such as polyparaphenylene terephthalamide, or inorganic. Among inorganic fibresglass fibres such as “E” or “S” can be used, or alumina, zirconia,silicon carbide, other compound ceramics or metals. A very suitablereinforcing fibre is carbon, especially as graphite. Graphite fibreswhich have been found to be especially useful in the invention are thosesupplied by Amoco under the trade designations T650-35, T650-42 andT300; those supplied by Toray under the trade designation T800-HB; andthose supplied by Hercules under the trade designations AS4, AU4, IM 8and IM 7.

Organic or carbon fibre is preferably unsized or is sized with amaterial that is compatible with the composition according to theinvention, in the sense of being soluble in the liquid precursorcomposition without adverse reaction or of bonding both to the fibre andto the thermoset/thermoplastic composition according to the invention.In particular carbon or graphite fibres that are unsized or are sizedwith epoxy resin precursor or thermoplast such as polyarylsulphone arepreferred. Inorganic fibre preferably is sized with a material thatbonds both to the fibre and to the polymer composition; examples are theorgano-silane coupling agents applied to glass fibre.

The composition may contain for example conventional toughening agentssuch as liquid rubbers having reactive groups, aggregates such as glassbeads, rubber particles and rubber-coated glass beads, filler such aspolytetrafluorethylene, silica, graphite, boron nitride, mica, talc andvermiculite, pigments, nucleating agents, and stabilisers such asphosphates. The total of such materials and any fibrous reinforcingagent in the composition should be at least 20% by volume, as apercentage of the total volume of the polyaromatic/thermoset mixture.The percentages of fibres and such other materials are calculated on thetotal composition after curing at the hereinbelow defined temperatures.

In a further aspect of the invention there is provided a process for thepreparation of a composition as hereinbefore defined comprising admixingthe respective polyaromatic and thermoset components as hereinbeforedefined and subsequently admixing the catalyst.

Preferably the composition is used in the form of a curable resincomposition as hereinbefore defined, made by mixing the polyaromatic,thermoset precursor and (at some stage) any fibrous reinforcing agentand other materials. A solvent may be present. The solvent and theproportion thereof are chosen so that the mixture of polyaromatic andthermoset resin precursor form at least a stable emulsion, preferably astable apparently single-phase solution. The ratio of solvent topolyaromatic is suitable in the range 5:1 to 20:1 by weight. Preferablya mixture of solvents is used, for example of a halogenated hydrocarbonand an alcohol, in a ratio suitably in the range 99:1 to 85:15.Conveniently the solvents in such a mixture should boil at under 100° C.at 1 atm pressure and should be mutually miscible in the proportionsused. Alternatively the polyaromatic and thermoset or precursor can bebrought together by hot melting and/or high shear mixing.

The mixture is stirred until sufficiently homogeneous. Thereafter anysolvent is removed by evaporation to give a resin composition.Evaporation is suitably at 50-200° C. and, at least in its final stages,can be at subatmospheric pressure, for example in the range 13.33 Pa to1333 Pa (0.1 to 10 mm Hg). The resin composition preferably contains upto 5% w/w of volatile solvent, to assist flow when used to impregnatefibres. This residual solvent will be removed in contact with the hotrollers of the impregnating machine.

After removal of residual solvent, the reactive catalyst is added ashort time prior to casting and curing or immediately prior to castingand cure.

The resin composition, possibly containing some volatile solvent alreadypresent or newly added, can be used for example as an adhesive or forcoating surfaces or for making solid structures by casting possibly in afoamed state. Short fibre reinforcement may be incorporated withcomposition prior to curing thereof. Preferably a fibre-reinforcedcomposition is made by passing essentially continuous fibre into contactwith such resin composition. The resulting impregnated fibrousreinforcing agent may be used alone or together with other materials,for example a further quantity of the same or a different polymer orresin precursor or mixture, to form a shaped article. This technique isdescribed in more detail in EP-A-56703, 102158 and 102159.

In a further aspect of the invention there is provided a process forcuring a curable composition as hereinbefore defined.

The curable resin composition of the invention may be cured in knownmanner. Suitably the composition in form of a resin solution or stableemulsion as hereinbefore described is transferred onto a suitable mouldor tool for preparation of a panel, prepreg or the like, the mould ortool having been preheated to a desired degassing temperature.

The stable emulsion is combined with any reinforcing, toughening,filling, nucleating materials or agents or the like, and the temperatureis raised to initiate curing thereof.

Suitably curing is carried out at elevated temperature up to 200° C.,preferably in the range of 60 to 200° C., more preferably at about70-190° C., and with use of elevated pressure to restrain deformingeffects of escaping gases, or to restrain void formation, suitably atpressure of up to 10 bar, preferably in the range of 3 to 7 bar abs.Suitably the cure temperature is attained by heating at up to 5° C./min,for example 2° C. to 3° C./min and is maintained for the required periodof up to 18 hours, preferably up to 9 hours, more preferably up to 6hours, for example 3 to 4 hours. Pressure is released throughout andtemperature reduced by cooling at up to 5° C./min, for example up to 3°C./min. Post-curing at temperatures in the range of 150° C. to 200° C.may be performed, at atmospheric pressure, employing suitable heatingrates to improve the glass transition temperature of the product orotherwise.

Curing may be in a single stage or in two stages, depending on selectedcure temperature and requirements of processing and product. For examplecuring may be conducted in an autoclave for the entire procedure, or forthe pre-cure only. In a first embodiment the method for curing acomposition as hereinbefore defined comprises in a single stagesubjecting the composition to elevated temperature and elevated pressurefor a period in excess of an hour, wherein temperature is in the range150-200° C., preferably 170-190° C. for a period in the range 4 to 7hours.

In a further embodiment the method for curing a composition ashereinbefore defined comprises pre-curing at elevated temperature andpressure for a period in excess of for an hour wherein the pre-curetemperature is in the region 60-150° C., preferably 70-145° C., morepreferably 80-135° C.

The pre-cure is preferably achieved by initially employing atime-temperature ramp as known in the art to achieve a desired precuretemperature.

It is surprisingly found that under these precure conditions thecomposition selectively reacts to promote chain extension reactions ashereinbefore described.

The precure is suitably carried out for a period of time from 1-18hours, preferably from 10 to 18 hours, more preferably from 12 to 5hours.

In a further aspect of the invention there is provided a pre-curedcomposition or pre-preg of a polyaromatic thermoplast and thermosetresin comprising a chain extended thermoplast as hereinbefore defined,hating number average molecular weight in the range 3,000-30,000,unreacted thermoset as hereinbefore defined and a catalyst ashereinbefore defined and optional reinforcement wherein the curedcomposition has a glass transition temperature in the range 50-70° C.and wherein the unreacted thermoset is present in an amount of up to 50parts by weight, for example 30 to 50 parts by weight.

The cured composition is surprisingly suited for post cure reaction ofthe remaining thermoset in the form of self reaction. It has been foundthat with some conventional compositions, further curing fails toadvance the properties of the material.

In a further aspect of the invention there is provided a method forpostcuring a pre-cured resin or pre-preg as hereinbefore defined atelevated temperature for a period of in excess of one hour wherein thetemperature is in the range of 150-200° C., preferably 170-190° C.

Postcuring may be at ambient or elevated pressure and is preferably atambient or slightly elevated pressure not requiring the use of anautoclave.

Without being limited to this theory it is thought that during the postcure the catalyst promotes self reaction, such as an etherificationreaction for example with an epoxy thermoset, which establishes thethermal and environmental properties of the resin. These can producecomposite materials with excellent mechanical properties, improvedenvironmental resistance over that of the state of the art materials andexcellent thermal properties. It is particularly surprising that thecompositions of the inventions are suited for distinct pre cure and postcure reactions under suitable conditions, the respective reactions beingselective at those conditions and providing a product architecture whichis well defined and well controlled and associated with specificadvantageous properties.

The post cure reaction is carried out with use of conventionaltime-temperature ramping as known in the art, and commencing at atemperature which does not exceed the Tg of the precured composition orpre-preg. The post cure is suitably carried out for a period of timefrom 1 to 8 hours, preferably 1 to 5 hours, more preferably from 1 to 3hours.

It has surprisingly been found that the precured composition or pre-pregof the invention has sufficient dimensional stability to enable postcuring without use of an autoclave or of moulds or tools used in theinitial reaction. This gives the freedom to conduct postcuring at highertemperatures without needing to take up autoclave space for furtherextended periods, and without subjecting moulds or tools to furtherelevated temperatures.

It is a particular advantage of the invention that low temperature cureenables use of composite tooling or moulds which can be readily andcheaply prepared and are suited to withstand the lower cure temperaturesemployed in the precure.

In a further aspect of the invention there is provided a method forcuring a curable composition as hereinbefore defined wherein thecomposition is formed in a composite tool or mould in the precure stageand subsequently removed from the tool or mould for post curing.

A further procedure comprises forming incompletely cured compositioninto film by for example compression moulding, extrusion, melt-castingor belt-casting, laminating such films to fibrous reinforcing agent inthe form of for example a non-woven mat of relatively short fibres, awoven cloth or essentially continuous fibre in conditions of temperatureand pressure sufficient to cause the mixture to flow and impregnate thefibres and curing the resulting laminate.

Plies of impregnated fibrous reinforcing agent, especially as made bythe procedure of one or more of EP-A56703, 102158, 102159, can belaminated together by heat and pressure, for example by autoclave,vacuum or compression moulding or by heated rollers, at a temperatureabove the curing temperature of the thermosetting resin or, if curinghas already taken place, above the glass transition temperature of themixture, conveniently at least 180° C. and typically up to 200° C., andat a pressure in particular in excess of 1 bar, preferably in the rangeof 1-10 bar.

The resulting multi-ply laminate may be anisotropic in which the fibresare continuous and unidirectional, orientated essentially parallel toone another, or quasi-isotropic in each ply of which the fibres areorientated at an angle, conveniently 45° as in most quasi-isotropiclaminates but possibly for example 30° or 60° or 90° or intermediately,to those in the plies above and below. Orientations intermediate betweenanisotropic and quasi-isotropic, and combination laminates, may be used.Suitable laminates contain at least 4 preferably at least 8, plies. Thenumber of plies is dependent on the application for the laminate, forexample the strength required, and laminates containing 32 or even more,for example several hundred, plies may be desirable. There may beaggregates, as mentioned above in interlaminar regions. Woven fabricsare an example of quasi-isotropic or intermediate between anisotropicand quasi-isotropic.

It has also been found that the cured materials present a well definedco-continuous morphology. The materials also demonstrate exceptionalfracture toughness properties (which has been shown to translate intocomposite). These values are higher than the conventional hightemperature cured material and are achieved using lower amounts ofthermoplast, for example up to 15% less thermoplast. A furthersurprising feature is solvent resistance properties of the materials.Neat resin samples immersed in dichloromethane at room temperatureabsorb less than 0.5% after 100 days. The conventional high temperaturecured resin would have absorbed in excess of 4% after such a period oftime.

In a further aspect of the invention there is provided a cured neatresin comprising a chain extended polyaromatic thermoplast anchored byreaction of reactive end groups within a thermoset network wherein theresin has a Tg in excess of 150° C., for example in the range 150-185°C., more preferably in the range 170-185° C., wherein up to 100% of thethermoset component is consumed in the reaction, for example 60-90% isconsumed.

In a further aspect of the invention there is provided a method forcuring cycle design for curing a composition as hereinbefore defined ina single cure stage or in pre and post cure stages. The cycle design maybe selected using known principles which apply in this case to thecompositions of the invention, and which are represented by anexponential relationship of time and temperature.

TABLE Illustrative cure cycles Precuring Precuring Post curingPostcuring temperature/° C. time/hours temperature/° C. time/hours  8514 180 2 (autoclave) (freestanding) 105 8 180 2 115 5.5 180 2 125 3 1802 135 1.5 180 2 — — 180 2

The method for curing cycle design may employ considerations such as geltime of composition, the risk of vacuum bag creep or rupture forstructures within autoclave for extended periods, autoclave lead time inparticular in industries requiring high production rates, and autoclaveoptimisation in cases that autoclaving prevents other components beingsimultaneously autoclaved.

In a further aspect of the invention there is provided a compositecomprising a post cured pre-preg as hereinbefore defined. The compositemay be provided in the form of a shaped article.

In a further aspect of the invention there is provided the use of acomposite tool or mould in a method as hereinbefore defined.

In a further aspect of the invention there is provided the use of acomposition, cured resin, composite or shaped product as hereinbeforedefined in the aerospace, marine or construction industry as a compositeor adhesive, or in the manufacture of an aeronautical, land or nauticalvehicle, building or commercial product or component thereof.

The invention is now illustrated in non limiting manner with referenceto the following examples.

EXAMPLE 1

Curable Compositions

The epoxies used were as follows;

-   MY0510—Trifunctional epoxy based on amino phenol-   PY306—A difunctional epoxy based on oligomers of Bisphenol F.

The principal curing agent used was that of 3,3′-diaminodiphenylsulphonewhich was co-cured with a number of LTC catalysts which were as follows;

-   BF₃(mea), BF₃ (dma), BF₃ (benzylamine), BF₃ (piperidine)-   Diuron, Chlorotoluron, Fenuron, CA150-   Curamid CN-   DICY.

The thermoplastic which was used to toughen the systems is commerciallyavailable as DDES (3,3′-bis(diamino diphenyl ether)sulphone, based on a40:60 PES:PEES Copolymer with primary amine termination synthesised byreacting 1 mole of DCDPS with two moles of m-Aminophenol using PotassiumCarbonate as the catalyst and Sulpholane as the reaction solvent.

EXAMPLE 2

Preparation of Compositions X99+0.5BF₃(dma)

Resin formulations were prepared by warming the two epoxies. Thetemperature of the epoxies was not allowed to exceed that of 60° C. Thethermoplastic resin, previously dissolved in a small amount ofDichloromethane, was then added in an amount of from 10-40 wt %. Oncethe resins had been warmed and their viscosity reduced theDiaminodiphenylsulphone was then added. The solvent was then removed at60° C. The DDS was dispersed by vigorous stirring. Prior to the pre curethe low temperature cure catalyst, BF₃(dma), was added and thoroughlydispersed within the resin which was cast as neat resin panels in amould, with evaporation of solvent. The samples were then cured at 85°C. over a period of time from 1 to 18 hours. The samples were thencharacterised by FTIR in order to determine the remaining epoxidecontent and the level of ether generated in the systems. A limitednumber of these samples were then post cured at 175° C. for 2 hours. Inorder to eliminate the temperature fluctuation of just turning the ovensup to 175° C. a ramp rate of 2° C. per minute, and several other ramprate effects were studied.

EXAMPLE 2.1

Preparation of Samples for Determination of Tg

The samples used for the FTIR study were also used to determine the Tgof the respective system. In some cases this meant employing the use ofDSC (in the case of liquid or soft materials). In the case's wherespecimens were hard at room temperature, Tortional Rheometry wasemployed. Specimens were cut from the FTIR samples whose dimensions were5 cm's in length, 1 cm in width and <2 mm in thickness. In some case'sDynamic Mechanical Thermal Analysis (DMTA) was used to determine thematerials glass transition temperature (Tg).

EXAMPLE 2.2

FTIR Equipment Used

Standard FTIR equipment was used which was capable of overlappingspectrums and calculating the level of ether and epoxide from the peakintensity. For the ether groups the peak at 1115 cm⁻¹ was assigned andfor the epoxide the peak at 912 cm¹ was assigned.

EXAMPLE 2.3

Neat Resin Mechanical Properties.

A neat resin screen was carried out in order to determine a range ofmechanical properties. Neat resin panels (6″*4″*3 mm) were preparedaccording to Example 2.

EXAMPLE 2.4

Neat Resin Morphology

Samples from panels prepared under 2.3 were examined by TEM to determinethe morphology of the respective system.

EXAMPLE 2.5

Solvent Uptake Experiments

Cured samples were prepared as neat resin discs which were about 2″ indiameter and about 3 mm thick. The neat resin samples were pre-dried,prior to immersion in solvent, at 135° C. for about 6 hours.

EXAMPLE 3.1

PREPARATION OF COMPOSITIONS X99+0.5BF₃(mea)

Formulations were prepared using the procedure of Example 2.

EXAMPLE 3.1.1

Neat Resin Mechanical Properties

For the above formulation 6″*4″*3 mm panels were prepared by curing theresin systems for 18 hours at 85° C. After cooling the panels wereplaced in a free standing air circulating oven and cured at 175° C. for2 hours using a ramp rate of 2C per minute.

The fully cured panels were then assessed using the following tests;

-   Fracture Toughness (G1c)-   Fracture Strength (K1c)-   Modulus-   Tensile Yield Strength-   Ductility Factor

Table I, details the results of the neat resin mechanical assessment andalso includes the results of a conventionally high temperature curedsystem.

TABLE I Tensile Fracture Fracture Yield Ductility Material ToughnessStrength Strength Factor Modulus X99* 0.67 1.34 127 0.11 3.1 X99** 0.291.09 117 0.06 3.0 X99 + 0.5 0.77 1.77 135 0.18 3.5 BF3 (mea)** X99TB +0.5 0.9  1.85 133 0.2  3.4 BF3 (mea)*** *Cured For 3 hours at 175 C.(20% Amine ended thermoplastic) **Cured For 18 hours at 85 C. and postcured for 2 hours at 175 C. (20% Amine ended thermoplastic) ***Cured for18 hours at 85 C. and post cured for 2 hours at 175 C. (23% Amine endedthermoplastic)

As can be seen from Table I the conventionally high temperature curedsystem produces the kind of neat resin fracture properties typical forthat level of thermoplastic. However when the same material is subjectedto a low temperature pre-cure of 18 hours at 85° C. followed by a postcure for 2 hours at 175 C the fracture properties are considerablylower.

If the same material is again cured at 85 and then post cured at 175 Cbut a low temperature catalyst (BF3(mea)) is incorporated then thefracture properties rise and in fact appear to be tougher than theconventional HTC system. This is increased further when additionalthermoplastic is added to the formulation.

EXAMPLE 3.1.2

Neat Resin Morphology (Transmission Electron Microscopy)—TEM

Annex I contains the TEM micrographs for all of the formulationsdetailed in Table I.

In the case of the X99** there is no visible evidence of a phaseseparated morphology. The neat resin fracture properties suggest thatthe system has not undergone a two phase separated system. In the caseof X99* the size of the phase separated morphology is below thedetection limit of the TEM technique. However the fracture properties ofthe material do suggest that a two phase system is present.

Observing X99**+0.5 BF3(mea) and X99TB***+0.5 BF3(mea) it can be seenthat a co-continuous morphology exists in both samples.

EXAMPLE 3.1.3

FTIR

Samples were prepared as detailed under Example 2 and then characterisedusing FTIR to determine the level of epoxy remaining and the amount ofether produced as a function of time the results of which can be seen inthe following Table's.

TABLE II Time at Ether/Aromatic 85° C. Ratio Epoxy/Aromatic Ratio %Epoxy Remaining X99 (Cured for x hours at 85 C.)  0 0.5  1.28 100   10.61  2 1.03 1.09 85  3 0.54 1.04 81  4 0.53 0.98 76  5 1.12  6 0.920.98 76  8 1.1  0.93 73 10 1.72 0.92 72 12 1.89 0.82 64 14 2.14 0.72 5618 2.47 0.68 53 Samples from Table II post cured for 2 hours at 175 C.using a 2 C./min ramp rate.  2 3.5 0.16 12.5  4 3.7 0.17 13    6 3.80.17 13    8 3.7 0.15 12   10 3.8 0.18 13.5 12 3.9 0.15 12  

TABLE III X99 (Cured for 3 hours at 175 C.) Time at 175° C. Ether/Epoxy/ (mins) Aromatic Ratio Aromatic Ratio % Epoxy Remaining  0 0.811.09 100   5 0.72 1.04 95 10 2.15 0.65 60 15 3.87 0.18 17 20 4.43 0.1817 25 4.31 0.15 14 30 4.2  0.15 14 45 4.2  0.14 13 75 4.1  0.15 14 904.22 0.15 14 105  4.19 0.15 14 120  4.2  0.18 17 135  4.21 0.15 14 150 4.45 0.13 12 165  4.66 0.12 11 180  4.5  0.13 12

TABLE IV Time at Ether/Aromatic 85° C. Ratio Epoxy/Aromatic Ratio %Epoxy Remaining X99 + 0.5 BF3 (mea) Cured at 85 C. as a function oftime.  0 0.61 1.13 100   1 1.71 0.77 68  2 2.01 0.72 64  3 2.12 0.7  62 4 2.27 0.66 58  5 2.49 0.66 58  6 2.51 0.63 56  8 2.5  0.57 50 10 2.580.52 46 12 2.67 0.52 46 14 2.96 0.46 41 16 3.2  0.43 38 18  3.2  0.43 38Samples from Table IV post cured for 2 hours at 175 C. using a ramp rateof 2 C./min.  2 3.6  0.2  19  4 3.43 0.2  18  6 3.67 0.17 15  8 3.380.18 16 10 3.52 0.16 14 12 3.34 0.19 17

Samples were pre cured at different temperatues and the results areshown in Figures I and II

As an indication of reaction, isothermal sweep and gel time weredetermined and the results are shown in Figure IIIa and IIIb.

EXAMPLE 3.1.4

Pre-cured and Post cured Tg's

Sample for the determination of Tg were prepared as described in 2.1 andwere determined using either DSC or Tortional Rheometry, depending uponthe physical nature of the specimen.

The HCT version of X99 was cured for 3 hours at 175 C and it's Tg wasdetermined using both Tortional Rheometry. The value for the Tg was inthe range of 170-180 C by DMTA and 170-180 C, using the value for G′, byTortional Rheometrics.

X99 and X99+0.5 BF3(mea) were subjected to a precure at 85 C as afunction of time and Tg data was collected. These samples were also postcured at 175 C for 2 hours using a ramp rate of 2 C/min. Table Vrepresents the Tg data for both the pre-cured and post cured specimens.

TABLE V X99 + BF3 X99 Time (mea) Time at 85 C. Tg (DSC) Tg (TR) at 85 C.Tg (DSC) Tg (Th) (Hours) Pre-cured Post cured (Hours) Pre-cured Postcured  4.5 −14.1 156  2 56 174  9.0 −6.0 156  4 55 178 13.5 6.7 157  665 176 18.0 24 156  8 69 178 12 88 177 18 98 176was subjected to a pre-cure at 85 C as a function of time and Tg datawas collected. These samples were also post cured at 175 C for 2 hoursusing a ramp rate of 2 C/min.

As can be seen from the above Table the addition of the 0.5 BF3(mea) hashad a significant effect upon the pre-cured Tg and has also had littleeffect upon the post cured Tg which is still in the region of 175 C, asobserved for the HTC cured system.

Samples were also precured at a range of temperatures as a function oftime and Tg data collected. The results are shown in Table VI

Time/ Tg (pre) Tg (post) Tg (pre) Tg (post) Tg (pre) Tg (post) hours105° C. 105° C. 115° C. 115° C. 125° C. 125° C. 4 75   151 5 76   14283.5 154 109 153 6 117 149 7 95.7 174 8 84.6 9 93   11  97.4

EXAMPLE 3.1.5

Solvent Uptake for X99+0.6 BF3(mea)

Figures IV shows results for Dichloromethane at 25 C−X99+0.6 BF3(mea).

Also included in Figures IV are the solvent uptake results for the X99system cured for 3 hours at 175 C. As can be seen from the results shownin that Figure, the addition of the BF3(mea) and the inclusion of thepre-cure hold have produced a post cured resin sample which hasexceptional resistance to Dichloromethane at 25 C.

Figures V shows results for water at 25C−X99+0.5 BF3(mea).

Similarly, Figures VI shows results for MethylEthylKetone at 25C−X99+0.5 BF3(mea)

The solvent uptake in all three solvents was identical for the X99TB+0.5BF3(mea). Solvent uptake was also investigated with dichloromethane,methyl ethyl ketone and water for discs and prepregs, includingdifferent prepreg lay ups: [0]16, [(0,90)4]s, [(+45, 0,−45,90)2]s, andcompared with commercial low temperature cure systems using curimidcatalyst. The system of the invention was found to show lower solventuptake in all cases, and in addition showed resistance to MEK whichappeared to chemically attack the comparison curimid system.

EXAMPLE 3.2

Preparation of Compositions X99+Alternative Boron Trifluoride Catalysts

The alternative BF3 catalysts which were considered were;

-   BF3(dma)-   BF3((bea)-   BF3(pip)

EXAMPLE 3.2.1

Neat Resin Mechanical Properties

Using the procedure of Example 2 fully cured panels were assessed usingthe tests outlined in Example 3.1.1;

Table VII, details the results of the neat resin mechanical assessmentand also includes the results of Example 3.1.1 and of a conventionallyhigh temperature cured system.

TABLE VII Tensile Fracture Fracture Yield Ductility Material ToughnessStrength Strength Factor Modulus X99* 0.67 1.34 127 0.11 3.1 X99** 0.291.09 117 0.06 3.0 X99 + 0.5 0.77 1.77 135 0.18 3.5 BF3 (mea)** X99TB +0.5 0.75 1.58 133 0.19 3.4 BF3 (dma)** X99TB + 0.5 0.8  1.82 133 0.213.5 BF3 (pip)** *Cured For 3 hours at 175 C. (20% Amine endedthermoplastic) **Cured For 18 hours at 85 C. and post cured for 2 hoursat 175 C. (20% Amine ended thermoplastic)

As can be seen from the above table the neat resin fracture propertiesare the same for all the three different types of BF3 catalyst.

Tests were also conducted comparing the post cured systems of theinvention having varied amounts of thermoplast up to 35 wt %. Toughnesswas found to increase at a greater rate above 15 wt % thermoplast andthis suggests a reaction effect is taking place with the catalyst inaddition to the expected increase by virtue of the additional tougheningthermoplast. At this level toughening was also found to be superior tothat in conventional high temperature cure systems.

EXAMPLE 3.2.2

Neat Resin Morphology (Transmission Electron Microscopy)—TEM

Annex 6 contains the TEM micrographs for all of the formulationsdetailed in Table VII. Observing X99**+0.5 BF3(mea). X99**+0.5 BF3(dma)and BF3(pip) it can be seen that a co-continuos morphology exists in allthree samples.

EXAMPLE 3.2.3

FTIR

Samples were prepared as detailed under Example 2 and then characterisedusing FTIR to determine the level of epoxy remaining and the amount ofether produced as a function of time the results of which can be seen inthe following Table's.

TABLE VIII X99 + 0.5 BF3 (dma) (Cured for x hours at 85 C.) Time atEther/Aromatic 85° C. Ratio Epoxy/Aromatic Ratio % Epoxy Remaining  00.38 1.28 100   1 1.49 0.87 70  2 1.36 0.9  72  3 1.95 0.83 66  4 1.980.75 60  5 2.37 0.74 59  6 2.05 0.76 61  8 2.41 0.69 55 10 2.84 0.63 5012 3   0.63 50 14 3.3  0.53 42 16 3   0.55 44 18 3.1  0.55 44

TABLE IX X99 + 0.5 BF3 (bea) (Cured for x hours at 85 C.) Time atEther/Aromatic 85° C. Ratio Epoxy/Aromatic Ratio % Epoxy Remaining  00.64 1.02 100   1 1.49 0.91 89  2 1.37 0.71 69  3 2.16 0.70 68  4 2.450.68 67  5 2.48 0.71 69  6 2.51 0.68 67  8 2.64 0.62 61 10 2.71 0.53 5212 2.84 0.45 44 14 2.8  0.46 45 16 3.23 0.46 45 18 3.47 0.46 45

EXAMPLE 3.2.4

Pre-cured and Post Cured Tg's

Samples for the determination of Tg were prepared as described in 2.1and were determined using either DSC or Tortional Rheometry, dependingupon the physical nature of the specimen.

Figure VII represents the pre-cured Tg's of the Boron Triflouridecatalysts used to cure X99. The Tg's are represented as a function ofpre-cure time in hours

As can be seen from Figure VII, after about 12 hours all the BF3 basedcatalysts produce pre-cured Tg's above 60° C.

Figure VIII represents the post cured Tg's of the materials described inFigure VII. As can be seen from that Figure, upon post cure all of theBF3 systems produce Tg's above 170° C.

Comparative Example 3.3

Preparation of Compositions

X99 cured with Curamid CN (Imidazole)

EXAMPLE 3.3.1

Neat Resin Mechanical Properties

Using the procedure of Example 2 fully cured panels were assessed usingthe tests outlined in Example 3.1.1;

Table X, details the results of the neat resin mechanical assessment andalso includes the results of Example 3.1.1 and of a conventionally hightemperature cured system.

TABLE X Tensile Fracture Fracture Yield Ductility Material ToughnessStrength Strength Factor Modulus X99* 0.67 1.34 127 0.11 3.1 X99** 0.291.09 117 0.06 3.0 X99 + 0.5 0.77 1.77 135 0.18 3.5 BF3 (mea)** X99+ 0.50.4  1.37 116 0.14 3.0 Curamid CN** * Cured For 3 hours at 175 C. (20%Amine ended KM180) **Cured For 18 hours at 85 C. and post cured for 2hours at 175 C. (20% Amine ended KM180).

The results from the above table show that the addition of the CuramidCN leads to an improvement in the toughness of the LTC X99 system but isstill only half that of the X99 system cured with 0.5 BF3(mea).

3.3.2 Morphology of X99 cured with Curamid CN.

The TEM micrograph in Annex 7 clearly show that there is visible sign ofa two phase system using this particular technique which is different tothat observed for the X99 system cured with anyone of the BF3 Lewisacids described.

EXAMPLE 3.3.3

FTIR

Sample were prepared as detailed under Example 2 and then characterisedusing FTIR to determine the level of epoxy remaining and the amount ofether produced as a function of time the results of which can be seen inthe following Table's.

TABLE XI X99 + 0.5 Curamid CN (Cured for x hours at 85 C.) Time atEther/Aromatic 85° C. Ratio Epoxy/Aromatic Ratio % Epoxy Remaining  00.52 0.98 100   1 1.2  0.83 85  2 2.76 0.84 86  3 2.63 0.77 78  4 3.130.75 77  5 3.34 0.64 66  6 4.43 0.51 52  8 5.61 0.49 50 10 6.7  0.49 5012 6.7  0.46 47 14 6.8  0.42 42 16 6.9  0.42 42 18 7   0.42 42

TABLE XII X99 + 1.0 Curamid CN (Cured for x hours at 85 C.) Time atEther/Aromatic 85° C. Ratio Epoxy/Aromatic Ratio % Epoxy Remaining  00.72 1.2  100   1 2.66 0.84 70  2 3.95 0.71 59  3 4.91 0.69 58  4 5.160.43 36  5 5.26 0.42 35  6 5.73 0.37 31  8 6.3  0.37 31 10 6.5  0.37 3112 6.7  0.36 30 14 6.9  0.35 29 16 7   0.33 27 18 7.2  0.31 26

The immediate difference between the data in the two tables abovecompared to the data in Table's II, III, VIII and IX (X99 cured with BF3based catalyst's ) is the level of ether which is produced. This isalmost double in the Curamid system. The appearance of large amounts ofether suggests that the epoxy moieties have reacted with each other.This leads to a highly crosslinked network.

Figure IX and X show the level of consumption of epoxide and the levelof ether generated from the data in Tables XI and XII respectively.

Figure X shows results for the consumption of epoxide as a function oftime at 85 C.

Figure X shows results for the generation of ether as a function of timeat 85 C.

EXAMPLE 3.3.4

Pre-cured and Post Cured Tg's

Samples for the determination of Tg were prepared as described in 2.3and were determined using either DSC or Tortional Rheometry, dependingupon the physical nature of the specimen.

TABLE XIII represents the precured Tg's for the X99 system cured with0.5 and 1.0 pbw of Curamid CN. Time of pre- X99 + 0.5 X99 + 1.0 cure at85 C. Curamid CN (Tg) Curamid CN (Tg)  0 −27   −27    4 50 43  6 51 45 8 50 43 10 52 45 12 51 42 14 50 41 18 52 43

TABLE XIV represents the post cured Tg's for the X99 system cured with0.5 and 1.0 pbw of Curamid CN. Time of pre- X99 + 0.5 X99 + 1.0 cure at85 C. Curamid CN (Tg) Curamid CN (Tg)  0 149 153  4 150 149  6 151 148 8 149 150 10 150 148 12 148 150 14 152 149 18 150 151

As can be seen from the two tables above that both levels of Curamid CNproduce pre-cured Tg's above 30 C. However their post cured Tg's do notrise above 160 C. The possible reason for this is that the Imidazolesreact via etherification reactions i.e. without amine consumption andchain extension and hence produce very tight crosslinked networks. Whenthis occurs under the precure conditions the system quickly becomes veryimmobile and is virtually ‘frozen’ from further chemical reactions. Asthe system post cures this ‘frozen’ state persists thus preventing onlya minimal increase in Tg. This is the complete opposite of what is foundin the case of the BF3(mea) were precure results in a Tg above 50 C butwith the minimum amount of etherification. Upon postcure it is stillrelatively mobile and can further react to produce much higher postcured Tg's.

EXAMPLE 3.4

Comparative Example—Alternative catalysts to Curamid CN.

A number of Imidazole and Urea based low temperature catalysts werecompared to see if they behaved like the Curamid CN or like the boronTriflouride catalysts.

The catalysts chosen were;

The alternative catalysts were initially examined by FTIR to establishthe rate of consumption of epoxide and the generation of ether.

The FTIR indicated that all of the Urea based catalysts behave exactlythe same as the Imidazole catalysts in that they react very quickly atlow temperatures to consume epoxide but their mechanism in doing so isto generate etherification. This leads to a highly crosslinked network,under pre-cure conditions, and results in a poor translation of high Tgduring postcure. These comments are confirmed from the following set ofdata derived from the curing of X99 with the above alternative Ureabased catalysts.

Pre-cured Tg's of X99 system cured with Diuron, Chlorotoluron, Fenuronand CA150.

Figure XI shows results for pre-cured Tg's as a function of time at 85C.

Similarly, Figure XII shows results for postcured Tg's of the abovepre-cured systems.

EXAMPLE 4

Preparation of Resin for Hot Melt Impregnation

Epoxy resins MY0510 and Rutapox 0158 were mixed together and heated.When the resin temperature reached 100-110° C. slow portion wiseaddition of thermoplastic polymer of Example 2 was commenced, with goodagitation to prevent formation of lumps. Heating of the mixture wascontinued to 130-135° C. with stirring until all the polymer wasdissolved, for approximately 30-45 minutes. The mixture was then cooledto 75° C. and the LTC catalyst, BF₃.mea was added in portions withefficient stirring. Mixing was continued for a few minutes until thecatalyst was dissolved. Pre-sieved 3,3′-DDS was added in portions withmixing for 5-10 minutes until the resin was homogenous. The resin wasdrained from the mixture, cooled immediately on chill plates and placedin a freezer at −18° C.

The epoxy resin precursors included 0.05% of a silicon oil de-foamer/airrelease agent such as Foamkill.

The resin was suited for hot melt impregnation to form composites whichwere tested and found to show equivalent or superior properties to thoseusing conventional catalysts.

1. Method for the preparation and curing of a curable composition or prepreg comprising at least one polyaromatic having reactive end groups, at least one thermoset resin, and a reactive catalyst, wherein the catalyst comprises a Lewis acid having amine functionality which co-ordinates the reactive end groups of the polyaromatic with the thermoset resin at a pre-cure temperature in the region 60-150° C., and wherein the at least one polyaromatic comprises at least one polyaryl sulphone comprising ether-linked repeating units, optionally additionally comprising thioether-linked repeating units, the units being selected from the group consisting of —(PhSO₂Ph)_(n)— and —(Ph)_(a) wherein Ph is phenylene, n=1 to 2, a=1 to 3 and when a exceeds 1, said phenylene are linked linearly through a single chemical bond or divalent group other than —SO₂— or are fused together, characterized in that the process comprises admixing the respective polyaromatic and thermoset components as hereinbefore defined, optionally in the presence of solvent, removing residual solvent by evaporation at 50-200° C., precuring in a first stage by subjecting the curable composition to a first lower temperature state in the range of 60-150° C. and in the presence of a BF₃ catalyst, and then subjecting said curable composition or prepreg to elevated temperature in the range of 60-200° C., with the use of elevated pressure of up to 10 bar to restrain deforming effects of escaping gases or to restrain void formation.
 2. Method as claimed in claim 1 comprising additionally post-curing in a second stage by subjecting the precured composition to a temperature in the range of 150° C. to 200° C. at atmospheric pressure, to improve the glass transition temperature of the product.
 3. Method as claimed in claim 2 wherein said post curing is carried out without use of an autoclave or of moulds or tools.
 4. Pre-cured composition or pre-preg comprising a chain extended polyaromatic in which reactive end groups are coordinated with a thermoset having number average molecular weight in the range 3,000-30,000, an amount of unreacted thermoset and a catalyst wherein the cured composition has a glass transition temperature in the range 50-70° C. and wherein the unreacted thermoset is present in an amount of up to 50 parts by weight made by the process of admixing a polyaromatic, wherein the polyaromatic comprises at least one polyaryl sulphone comprising ether-linked repeating units, optionally additionally comprising thioether-linked repeating units, the units being selected from the group consisting of —(PhSO₂Ph)_(n)— and —(Ph)_(a)— wherein Ph is phenylene, n=1 to 2, a=1 to 3 and when a exceeds 1, said phenylene are linked linearly through a single chemical bond or divalent group other than —SO₂— or are fused together, and thermoset components, optionally in the presence of solvent, removing residual solvent by evaporation at 50-200° C., precuring in a first stage by subjecting the curable composition to a first lower temperature state in the range of 60-150° C., and then subjecting said curable composition or prepreg to elevated temperature in the range of 60-200° C., with the use of elevated pressure of up to 10 bar to restrain deforming effects of escaping gases or to restrain void formation. 